The Wilderness Retreat by Jennifer Moore

When Bella drops her son at University, she heads to a retreat centre in Scandinavia, a treat paid for by her sister and the perfect opportunity to reset and think about her new life and future. The centre is beautiful, although remote. She is introduced to the other people she'll spend the week with when she arrives. 

However, strange things start to happen, including notes under her door and weird scratching in the walls. Bella grows suspicious about whether someone is deliberately targeting her. She shrugs it off, but as the week progresses, things get worse when a guest speaker invited to the centre turns out to be someone from Bella's past whom she never wanted to meet again. Add to this stormy weather and fallen trees, and we have an Agatha Christie style mystery where no one can leave the centre, and everyone falls under suspicion. Bella grows ever fearful of the other guests and which of them may wish to harm her and why. Bella's credibility is tested, and she becomes isolated and ostracised. 

I won't say any more for fear of spoiling the story. 

It played out well, and I enjoyed the final reveal.

This moves along at a good pace, and I found it very entertaining.